The present invention relates to the formation of lipid vesicles, e.g., paucilamellar lipid vesicles, using blended lipids. These vesicles have as the major lipid a waxy or oily material which, in an unblended state, forms neither a lamellar phase nor vesicles. More particularly, waxy or oily materials such as fatty alcohols, glyceryl mono- and diesters of long-chain fatty acids, and glycol monoesters are used, in combination with other materials which may or may not form lamellar phases or vesicles, to form stable vesicles. These vesicles are particularly useful for cosmetic and pharmaceutical applications.
U.S. Pat. No. 4,911,928, discusses a broad variety of materials which may be used to form oil-filled lipid vesicles. All of the materials discussed in the aforementioned patent, the disclosure of which is incorporated herein by reference, will form vesicles by themselves when hydrated. However, certain additives, like charge-producing agents or sterols such as cholesterol, may be included in the vesicular structure. U.S. Pat. No. 4,917,951, the disclosure of which is also incorporated herein by reference, discloses a class of materials which cannot form vesicles unless a sterol such as cholesterol is added. However, all of the materials described in both of these patents, as well as the patents cited therein such as the Vanlerberghe U.S. Pat. No. 4,217,344, concerning materials which form vesicles without the addition of a second structural lipid. In fact, many of these materials may be able to form a lamellar phase under proper conditions, as described in the Vanlerberghe U.S. Pat. No. 4,217,344.
However, many cosmetic preparations include compounds which form neither vesicles nor a lamellar phase. These include the C.sub.12 -C.sub.18 fatty alcohols (which are used to provide "feel" to certain cosmetics), glycol stearate a common thickener), glyceryl mono- and distearate (which are used as emulsifiers), and glyceryl dilaurate (which is often used in dermatologicals). Since cosmetics and dermatologicals are one of the most rapidly expanding fields for the use of lipid vesicles, it would be logical to attempt to use as the vesicle formers amphiphiles which are commonly incorporated in the cosmetics. However, these amphiphiles cannot be made into vesicles using either using conventional techniques, or even those techniques described in U.S. Pat. No. 4,911,928. These materials are either water soluble so that they cannot form vesicles or a lamellar phase, or they are so oily or waxy that they can only be formed into emulsions, e.g., they do not hydrate sufficiently well for vesicle formation. In fact, these materials do not form vesicles even with standard additives such as cholesterol or charge-producing agents.
Accordingly, an object of the invention is to provide a method of making lipid vesicles using as a primary or major structural lipid of the bilayers a lipid which will not form vesicles in an unblended state.
Another object of the invention is to provide lipid vesicles having two or more lipids blended to form the lipid bilayers, at least one of which will not form a lamellar phase or vesicles in an unblended state.
A further object of the invention is to provide a method of forming lipid vesicles using cosmetic, pharmaceutical, or dermatologically useful substances as the primary vesicle formers.
These and other objects and features of the invention will be apparent from the following description.